Chlorine dioxide is known to be an excellent disinfectant as well as a strong oxidizing agent. Its bactericidal, viricidal, algicidal, fungicidal, bleaching, and deodorizing properties are well documented in the prior art. Also known to the prior art is the difficulty of storing and transporting chlorine dioxide, resulting in various apparatuses and compositions to accomplish the on-site production of chlorine dioxide.
Generators for the on-site production of chlorine dioxide in large scale applications such as treating drinking water or industrial process water are well known. An example of such a generator is disclosed in U.S. Pat. No. 4,247,531. However, such generators do not lend themselves to small scale, long term controlled release of chlorine dioxide such as is necessary in the preservation of boxed citrus fruit during shipping or in deodorizing enclosed spaces such as refrigerators or lockers.
For small scale applications, stabilized chlorine dioxide solutions or metal chlorite solutions that liberate chlorine dioxide when acidified, are known in the art. One method of producing a stabilized chlorine dioxide solution is disclosed in U.S. Pat. No. 3,123,521. Other, slightly different methods of producing these solutions are disclosed in U.S. Pat. No. 3,278,447 and U.S. Pat. No. 3,271,242. In certain small scale applications, such as the protection of plant or animal products from bacterial and fungal attack during the shipping and storage of such products, these liquid products are disadvantageous because of the difficulty in packaging and application as well as the danger of contamination of the food products due to spillage. Another disadvantage of such solutions is the fact that they must be acidified in order to release chlorine dioxide. Yet another disadvantage is the difficulty in controlling the rate of release of chlorine dioxide which often results in unacceptably high concentrations of the chlorine dioxide gas.
Powdered or dry compositions that release chlorine dioxide upon addition of water might be considered able to solve the foregoing problems associated with stabilized chlorine dioxide or metal chlorite solutions. Such dry compositions are disclosed in U.S. Pat. No. 2,071,091; U.S. Pat. No. 2,071,094; U.S. Pat. No. 2,022,262; and U.S. Pat. No. 2,482,891. However, these prior art dry compositions do not provide for a dry diluent to control release rates and they are accordingly prone to uncontrolled overproduction of chlorine dioxide. In addition, these prior art compositions must be mixed with water or water vapor in order to generate chlorine dioxide. The water addition step effectively imparts to these dry compositions the same limitations and disadvantages of the liquid solutions mentioned above.
A method of adsorbing sodium chlorite solutions or chlorine dioxide solutions onto a dry, powdered adsorbant that releases chlorine dioxide in the presence of a powdered, hydrated acid at a pH of less than about 6 is disclosed in U.S. Pat. No. 3,591,515 and the Japanese counterpart, Japanese Pat. No. 48-32079. However, this method of producing a dry chlorine dioxide release composition and the resultant chlorine dioxide release compositions have many drawbacks. Although the foregoing are disclosed as substantially dry compositions, it is obvious that an energy intensive drying step must be involved since the chlorite solutions utilized are only 6% in concentration, close to 90% of the solution being water. Another drawback of these compositions is that the amount of chlorite or latent chlorine dioxide available is limited to the amount of pulverent adsorbant is capable of adsorbing so that the amount of chlorine dioxide available is limited. Another drawback of such compositions is that, since the chlorine dioxide or sodium chlorite solutions are adsorbed onto the dry adsorbant uniformly, all the adsorbant material has chlorite on it. Accordingly, when such materials are mixed with a powdered, hydrated acid material, all of the acid material will be in contact with adsorbant containing chlorite, thereby resulting in an uncontrolled release of chlorine dioxide.